Aqueous developable photosensitive polyurethane-(meth)acrylate

ABSTRACT

A photopolymer useful in preparing water-developable, solid printing plates is prepared by preparing a urethane prepolymer by reacting polyoxyalkylene diols or polyester diols, or a mixture thereof, with an excess of diisocyanate, followed by chain extending the resulting prepolymer mixture with an alkyldialkanolamine, then reacting the chain-extended product with a hydroxyalkyl(meth)acrylate. The resulting photopolymer is suitably formulated with additional photoactive (meth)acrylate monomers or oligomers and photoinitiator for casting or extrusion on a substrate to form a flexographic printing plate. Following UV exposure of the plate through a negative, unexposed areas can be removed by washing with a slightly acidic aqueous medium, to give a plate with a desirable relief image. The use of the aqueous washout solution as opposed to organic solvents minimizes pollution problems.

This application is a continuation-in-part of our copending applicationU.S. Ser. No. 924,264 filed Aug. 3, 1992 for "Aqueous DevelopablePhotosensitive Polyurethane(meth)acrylate", incorporated herein byreference in its entirety.

RELATED APPLICATION

U.S. Ser. No. 662,699, filed Mar. 1, 1991, now U.S. Pat. No. 5,290,663Truc-Chi Thi Huynh-Tran, owned by the common assignee hereof, isdirected to aqueous developable photocurable compositions.

FIELD OF THE INVENTION

This invention relates to radiation curable polymers and formulations orcompositions containing them, as well as photosensitive articles havingsolid surfaces or layers prepared from such polymers or formulations.The invention also relates to a process for making and using thepolymers and making and using the photosensitive articles.

BACKGROUND OF THE INVENTION

Photocurable polymers and compositions are well known in the art forforming printing plates and other photosensitive or radiation sensitivearticles. In the field of radiation sensitive flexographic printingplates, the plates typically comprise a support and a photosensitivesurface or layer from a photocurable composition. Additional layers orsurfaces on the plate include slip and release films to protect thephotosensitive surface. Prior to processing the plate, the additionallayers are removed, and the photosensitive surface is exposed toradiation in an imagewise fashion. The unexposed areas of the surfaceare then removed in developer baths.

Removal of unexposed surfaces comprising solid photocurable compositionssuch as those disclosed in U.S. Pat. No. 2,760,863 require the use ofdeveloper baths comprising environmentally unsafe, organic solvents suchas tetrachloroethylene, 2-butanone, benzene, toluene, xylene,trichloroethane and solvent mixtures such astetrachloroethylene/n-butanol. However, due to the toxicity, highvolatility and low flash point, their use gives rise to hazardousconditions and creates pollution problems. Thus, recently there has beena strong interest in the field to develop photosensitive layers innon-organic solvent developing solutions, e.g., aqueous,surfactant-aqueous or alkaline-aqueous solutions. However, thecompositions resulting from recent attempts to achieve aqueousdevelopable plates demonstrate deficiencies in mechanical properties,e.g., flexibility. See European Application 261,910.

For instance, in addition to possessing an aqueous developablephotosensitive surface, a flexographic printing plate must havesufficient flexibility to wrap around a printing cylinder, yet be strongenough to withstand the rigors experienced during typical printingprocesses. Further, the printing plate should be soft enough tofacilitate ink transfer during printing.

Previous aqueous developable compositions have not possessed all thedesirable features such as flexibility, softness and solvent resistanceto inks typically used in printing. For example, U.S. Pat. No. 4,023,973describes a photosensitive composition comprising a maleic anhydrideadduct of a 1,2-polybutadiene. However, because the 1,2 content of thismaterial is very high, i.e., 70% or more, this composition has anundesirably high rubber hardness.

Furthermore, other water-developable photosensitive compositions whichcontain as the main component a high molecular weight polymer such aspolyvinyl alcohol, cellulose, polyethylene oxide, or the like, areinsufficient in flexibility and possess a high degree of rubber hardnessand hence are unsuitable for use in flexographic printing plates.

Finally, it is also important that the photosensitive surface of theprinting plate be dimensionally stable during storage. For example, somecompositions used for making plates have shown inferior stabilityproperties when used in solid flexographic printing plates in that thecompositions become tacky and pasty during storage. Those inferiorproperties have been attributed to the low molecular weight of thepolymers used to prepare the printing plates. See U.S. Pat. No.4,762,892 to Koch et al. and discussion of low molecular weight polymersdisclosed in Japanese Kokoku 57-23693.

Photosensitive formulations using the polymers of this invention arewater-developable without presenting any of the aforesaid disadvantages.

Japanese Kokai Pat. (A), SHO 59-113430, Disclosure Date Jun. 30, 1984,Sakurai et al., discloses a water-developable printing plate made with alight-sensitive polymer. The polymer is made by chain extending both anisocyanate end capped polyester diol, and anisocyanate-hydroxyl(meth)acrylate adduct with an alkyl diethanolamine.Thus, a chain extended prepolymer terminated with isocyanate (such asPrepolymer III herein) is not made. The final polymer product isquaternized to increase cure speed. The present invention does notrequire this step. The solid photopolymer IV of the instant invention isnot made. In Example 2 of the reference (which appears to be typical ofthe reference Examples), a mixture of an isocyanate end-capped polyetherdiol (PEG 1000) and a diisocyanate-hydroxyalkyl(meth)acrylate adduct ischain-extended with N-methyldiethanolamine under conditions leaving nodetectable -NCO.

European Pat. Application 54,150, filed Oct. 23, 1981, Lehner et al.,assigned to BASF, describes a UV-activatable polymer made by firstreacting together three components, i.e., a polyether diol,diisocyanate, and alkyldialkanolamine, and reacting that product with anepoxy acrylate. The final polymer product is formulated conventionallywith acrylates and photosensitizers for use in water-developableprinting plates. Since this reference describes a polymer comprisingmoieties of polyether diol, diisocyanate, alkyldialkanolamine, andacrylate, it is appropriate to consider it at length. In the Lehner etal. reference the product is a random copolymer consisting of randomlypositioned moieties of polyether polyol, diisocyanate,alkyldialkanolamine, and epoxy-acrylate in various combinations, e.g.,B-A-B, B-C-B, B-A-B-C-B, B-A-B-C-B-D-B, etc., where A is polyether diol,B is diisocyanate, C is alkyldialkanolamine and D is an epoxy acrylate.This introduces pendant acrylate groups along the polymer chain.Finally, polymer viscosity is increased to obtain a solidpolyurethane-urea by addition of a diamine which forms urea linkages.Lehner et al. did not react epoxy-acrylate sequentially. All A, B, C,and D were added at the same time. The Lehner et al. reference does notdisclose an isocyanate end-capped polyether diol or polyester diol,chain extended with an alkyl dialkanolamine, with the chain-extendedproduct further end-capped with hydroxyalkyl(meth)acrylate.

This invention differs in other important ways from the Lehner et al.process. (1) It is sequential, that is, the diol is end-capped, thenchain-extended at a point in the process prior to terminating withacrylate. (2) The resulting molecule is then terminated with acrylate,whereas the reference reacts an epoxy-acrylate to form pendant groupsalong the polymer chain. (3) This invention does not utilize urealinkages. (4) This process does not quaternize with glacial acetic acidto make an ionomer. These differences ensure a precise and highlydesirable thermoplastic polyurethane elastomer. That is, a structurethat will provide the correct predetermined molecular weight andcomposition and will necessarily result in a printing plate with goodphysical properties and good aqueous and oil based ink resistance. Thereference does not make the products of the instant invention.

U S Pat. No. 5,069,999, Higashi et al., "PS Plate for MakingLithographic Plate Requiring No Dampening Water," (1991), discloses aprinting plate comprising a photosensitive mixture comprising anacrylate monomer or oligomer and a polyurethane resin made ". . . byreacting a diisocyanate with approximately equimolar amount of a diol orthose obtained by reacting a diol with a slight excess of a diisocyanateand then subjecting the reaction product to a chain extending reactionwith a diamine, a diol, or water." [Emphasis supplied.] (Col. 4, line66--Col. 5, line 2.) The reference does not make a solid photopolymer,nor does it discuss or disclose water developability. Further,prepolymer III of the instant invention (a unique chain-extendedpolyurethane) is not disclosed in the reference. The reference suggestsusing alkyldialkanolamine or dihydroxy(meth)acrylate as a diol (Col. 5,lines 37-39). However, the reaction of a hydroxyalkyl-(meth)acrylatewith a diisocyanate end-capped polyether diol further chain-extendedwith alkyldialkanolamine (Polymer IV of the instant invention) is notdisclosed in the reference.

U.S. Pat. No. 4,888,379, Henning et al., "Heat-Sensitive PolyurethaneDispersions," (1989) discloses (Example 2) reacting a mixture ofpolycarbonate polyol and polyethylene oxide-polypropylene oxidepolyether polyol with hexamethylene diisocyanate, followed by chainextending the resulting polyurethane with methyldiethanolamine (MDEA).The resulting material was further extended with isophorone diamine inwater to form a polyurethane latex or emulsion useful for coatings. Thefinal polyurethane emulsion is not photocurable.

U.S. Pat. No. 4,113,592, Rybny et al., "Trihalogenated Hydrocarbons asCo-Photoinitiators," (1978), teaches the addition ofmethyldiethanolamine to known photosensitizers to increase cure rate inphotosensitizer compositions.

U.S. Pat. No. 4,980,108, Suzuki et al., "Process for Forming aPolyurethane Coated Biaxially Oriented Polyester Film," (1990) teachesintroduction of pendant carboxylic groups into a polyurethane prepolymerfollowed by neutralization with methyl diethanolamine.

U.S. Pat. No. 4,003,751, Carder, C.H., "Coating and Ink Compositions,"(1977), teaches reacting together a hydroxy(meth)acrylate, amonohydroxylamine, and an organic diisocyanate all in one step. Theresult is a mixture of polyurethanes formed from thehydroxy(meth)acrylate and hydroxylamine reacting separately with thediisocyanate. The reaction of a hydroxy(meth)acrylate withchain-extended isocyanate end-capped polyether and/or polyester diols isnot disclosed.

U.S. Pat. No. 4,210,713, Sumiyoshi et al., "Photo-Curable Compositionfor Coating Containing an Unsaturated Urethane Modified Polymer,"(1980), discloses a photopolymer made by reacting a diisocyanate with anacrylate. The acrylate can be the mono(meth)acrylic ester ofN-methyldiethanolamine.

U.S. Pat. No. 3,864,133, Hisamatsu et al., "Photo-PolymerizableCompositions," (1975), discloses reacting, in specified sequence, adiisocyanate, a polyol, and an acrylate ester, optionally with an amine(e.g., methyldiethanolamine). The amine is said to accelerate hardeningin the presence of air. In Example 6 tolylene diisocyanate was reactedwith trimethylolpropane, and the result was reacted further withethylacrylate and 2-hydroxyethylacrylate, followed by addition oftriethanolamine. A mixture of acrylates was added as physical diluentsto make the final photopolymer mixture. Example 49 discloses thereaction of tolylene diisocyanate with a polyester polyol, followed byreacting the resulting polyurethane with a mixture of methylmethacrylate and hydroxyethylmethacrylate. The result was mixed withtriethanolamine. The sequential reaction of diisocyanate plus polyetherand/or polyester diols followed by chain extension withalkyldialkanolamine, followed by reacting withhydroxyalkyl(meth)acrylate is not disclosed.

U.S. Pat. No. 4,606,994, Illers et al., "Process for ProducingPhoto-cured Printing Plates Possessing a Defined Hardness," (1986)discloses reacting together a polyurethane with an acrylate to putacryloyl side groups on the polyurethane, optionally in the presence ofdialkanolamine as chain extender. Prepolymer III and Photopolymer IV ofthe instant invention (as hereinafter described) are not made. Examples1-3 describe polyether urethane possessing acrylate side groups preparedfrom polyethylene oxide polyol, bisphenol-A diglycidyl ether diacrylate,butanediol, cyclohexanedimethanol and hexamethylene diisocyanate. Chainextension of an isocyanate end-capped polyether or polyesterdiol with analkyldialkanolamine followed by reaction with ahydroxyalkyl(meth)acrylate is not disclosed. Furthermore, the resultingphotosensitive plates were developed in alcohol/water mixtures, whichare less environmentally safe than this invention which uses dilutesolutions of water and surfactants, vinegar or citric acid.

U.S. Pat. No. 4,716,094, Minonishi et al., "Photosensitive ResinComposition Which is Improved with Respect to Surface Tack-FreeCharacteristic after Curing, and a Method," (1987) suggests (Col. 5)reacting an isocyanate end-capped polyether polyol with a compoundhaving a hydroxyl, carboxyl, or amino group containing unsaturatedcarboxylic acids or esters to prepare a printing plate prepolymer.

Japanese Kokai Pat., HEI 2-1859, disclosure date, Jan. 8, 1990, Kawaharaet al., "Photosensitive Resin Composition," discloses making aphotopolymer with a softening point of 45-80° C. to enhance waterdevelopability. This is disclosed to be accomplished by reacting adiisocyanate-capped polyether diol with hydroxyethylmethacrylate. Chainextension with alkyldialkanolamine to form a thermoplastic elastomerpolyurethane is not used in the process.

Japanese Kokai Pat. (A), HEI 2-4255, of Jan. 9, 1990, Satomi et al.,"Light-Sensitive Composition," discloses preparation and use of aurethane acrylate polymer similar to that of Japanese Kokai Pat. HEI2-1859, above, except that a polymeric material is added mechanically toregulate elasticity and hardness after photoexposure.

European Pat. No. 0 367 086 of Jan. 25, 1989, Littmann et al., assignedto BASF AG, discloses a water developable printing plate using acarboxylated polymer with acrylate-terminated chains. Diisocyanate isnot used.

European Pat. Application, Publication No. 0 351 628 A2, of Jul. 4,1989, Gersdorf et al., "Photosetting Elastomer Mixture and RecordingMaterial Obtained from It for the Production of Relief Printing Plates,"assigned to Hoechst AG, discloses a polyurethane base polymer graftedwith a vinyl carboxylate which is later saponified to form acid groupsand admixed with acrylates and photosensitizer to make awater-developable printing plate. There are no alkyldialkanolamine oracrylate groups in the base polyurethane chain.

In European Patent 374,707 of Dec. 13, 1989, Gersdorf et al.,"Photocurable Elastomer Mixture Containing Polyurethane, UnsaturatedMonomer and Initiator, Useful for Printing Plate and PhotoresistProduction," assigned to Hoechst AG, the mixture formulated for printingplates comprises polyurethane grafted with a vinyl carboxylate, plusacrylate diluent and photosensitizer. The exposed plate iswater-developable.

Japanese Kokai Pat. (A), HEI 2-46460, of Feb. 15, 1990, Tomita et al.,"Light Sensitive Resin Composition," discloses a polyurethane prepolymertreated with dimethylolpropionic acid to yield a further polyetherurethane, which, with other polyether urethanes, is mixed with acrylateand photosensitizer in the preparation of a water-developable plate. Thebase photopolymer molecule did not contain either alkyldialkanolamine oracrylate.

Xiao, H.X., et al., "Urethane Ionomers," 32nd Annual PolyurethaneTechnical Marketing Conference, Oct. 1-4, 1989, pp. 398-411, disclosesreacting diisocyanate with polyether diol, followed by reaction withmethyldiethanolamine until the mixture showed zero cyanate. Theresulting chain-extended prepolymer thus had no molecules terminated byisocyanate, as required in Prepolymer III of the instant invention, andthe final polyurethane does not contain any photocurable sites.

Speckhard, T.A., et al., "Properties of Segmented PolyurethaneZwitterionomer Elastomers," J. Macromol. Sci.-Phys., B 23 (2), 175-199(1984), discloses (Scheme 1, p. 178), the reaction ofmethyldiethanolamine directly with isocyanate-capped polyether diol inthe absence of free diisocyanate. No polyurethane prepolymer of the typediisocyanate/methyldiethanolamine/diisocyanate is made, as required inthe instant invention, and the product as chain-extended withmethyldiethanolamine is shown as terminating in hydroxyl, notisocyanate. And there is no acrylate terminator. The final polymer isnot a photopolymer.

Show-an Chen, et al., "Polyurethane Cationomers, I. Structure-PropertyRelationships," Journal of Polymer Science, Part B: Polymer Physics,Vol. 28, 1499-1514 (1990), discloses (p. 1500) reacting polyether diolwith an excess of toluene diisocyanate, followed by reaction withmethyldiethanolamine, until the reaction mixture tests zero isocyanate,thus indicating absence of isocyanate terminated molecules. (The instantinvention requires isocyanate terminated prepolymer at this stage,defined as Prepolymer III. There are no acrylate groups in the referencepolymer.

Miller, J.A., et al., "Properties of Polyether-Polyurethane Anionomers,"J. Macromol. Sci.-Phys., B 22 (2), 321-341 (1983). This referencediscloses (p. 325) end-capping polyether polyol with an excess ofdiisocyanate, followed by chain extension with methyldiethanolamine. Thelatter reaction is continued until the reaction mixture shows zeroisocyanate, thereby forming a prepolymer without terminal isocyanategroups. (At this stage the instant invention requires isocyanateterminated prepolymer Prepolymer III, as hereinafter defined.)

Hsieh, K.H., et al., "Effect of Charge Groups in Polyurethane Ionomersand Blends," Adv. Urethane Sci. Technol., vol. 10, pp. 77-83 (1987).Page 79 discloses casting a physical mixture of isocyanate cappedpolyether polyol and methyldiethanolamine in a mold at 70° C.

Hsu, S.L., et al., "Polyurethane Ionomers. I. Structure-Properties;Relationships of Polyurethane Ionomers," Journal of Applied PolymerScience, Vol, 29, 2467-2479 (1984), describes end-capping polyether diolwith diisocyanate, followed by reaction with methyldiethanolamine. Thereaction was stopped when the reaction mixture showed zero isocyanate(p. 2468), indicating that the resulting prepolymer was not terminatedwith isocyanates. (At this stage the instant invention requiresisocyanate terminated prepolymer, Prepolymer III as hereinafterdefined.) Preparation of a photocurable polymer with acrylate groups wasnot disclosed.

Encyclopedia of Polymer Science and Engineering, John Wiley & Sons(1988), 2d Ed., Vol. 13, pp. 259-261, discloses the general reaction ofisocyanates with polyester polyols to form polyurethanes.

SUMMARY OF THE INVENTION

A polyether diol (polyoxyalkylene diol) optionally with a polyester diolis end-capped with an excess of a diisocyanate, the resulting isocyanatecapped polyurethane is chain-extended with a alkyldialkanolamine, andthe chain-extended polymer is reacted with hydroxyalkyl(meth)acrylate toterminate the polymer chains with (meth)acrylates. One of ordinary skillin the art will recognize that, in addition to the polyether diols andthe polyester diols discussed above, various blends of diols may beutilized. The final polymer product is photosensitive (photocurable) andcan be formulated with photosensitizer and (meth)acrylate diluents tomake water-developable printing plates, photoresists, and the like.

Key features of the invention include (inter alia):

(1) The final photopolymer is a solid. This means there is no cold flowin formulated printing plates, which remain dimensionally and thermallystable.

(2) The photopolymer synthesis uses an alkyl dialkanolamine, therebyintegrating an amine into the polymer chain, resulting in waterdispersibility.

(3) The photopolymer has terminal (meth)acrylate groups for UVcurability.

OBJECTS OF THE INVENTION

It is an object of the invention to prepare a novel solidwater-dispersible polymer of predetermined sequentially designedstructure which can be crosslinked or cured by exposure to actinicradiation.

A further object is to make a water-developable storage-stableflexographic relief printing plate.

A still further object is to make a printing plate that can be developedin aqueous solutions that are harmless to the environment.

Another object is to synthesize a solid water-dispersible, UV-sensitivepolymer suitable for printing plate use wherein elements that providewater-dispersibility and UV-sensitivity are in the same molecule.

It is an object of the invention to provide a photosensitive articlecomprising a novel photocurable composition.

Another object is to synthesize a novel urethane prepolymer (hereinPrepolymer III, or simply III) especially designed for reaction with ahydroxyalkyl(meth)acrylate.

Another object is to provide a novel (meth)acrylate-terminatedpolyurethane (herein, Photopolymer IV, or simply IV).

Another object is to chain-extend an isocyanatecapped polyether diol orisocyanate-capped polyester diol or mixture thereof, withalkyldialkanolamine, followed by terminating the resulting polymer chainby reaction with hydroxyalkyl(meth)acrylate.

Another object is to prepare a flexographic relief printing plate thatwill not swell unduly in conventional aqueous- or oil-based inks.

Unless otherwise indicated the term "(meth)acrylate" means eitheracrylate or methacrylate.

Molecular weights are number average, M_(n), as determined by GelPermeation Chromatography using polystyrene standards.

DETAILED DESCRIPTION Overview

The main reactions and products involved in the invention are givenschematically and simplistically as follows:

1.P+Cy→(Cy--P)_(x) --Cy (I);

2.N+Cy→(Cy--N)_(y) --Cy (II);

3.I+N+II→[(Cy--P)_(x) --(Cy--N)_(y) ]_(z) --Cy (Prepolymer III, or III);(Note: Reactions 2. and 3. go forward together.)

4.III+A→A--[(Cy--P)_(x) --(Cy--N)_(y) ]_(z) --Cy--A (Photopolymer IV, orIV,

where P is a polyether diol or polyester diol or their moieties, Cy is adiisocyanate or its moiety, N is an alkyldialkanolamine or its moiety,and A is a hydroxyalkyl(meth)acrylate or its moiety. In these reactionshydroxyl containing compounds are linked to diisocyanate containingcompounds via urethane linkages, --NH--C(:O)--O--, to form therespective moieties. x, y, and z may differ from molecule to molecule,but are such that the over-all molecular weight of Prepolymer III,whether made from polyether diol or polyester diol or their mixtures, asin the range of about 5,000-60,000 (preferably about 5,000-30,000), andthat of Photopolymer IV is in the range of about 5,000-60,000(preferably about 7,000-40,000). Segments of I and II may be positionedrandomly in the chain.

The aforesaid 4 reactions may be restated explicitly. In thisrestatement the mole ratio of P:Cy:N:A must be 1:1.3-8:0.2-7:0.1-3,preferably 1:1.5-6:0.4-5:0.2-1.

Depending on the molecular weight of the polyols (in this casepolyether, polyester, polycaprolactone or polycarbonate polyols ormixtures of polyols), it is preferable to select the molar ratio of thereactants P (for polyols), Cy (for diisocyanate), N (foralkyldialkanolamine) and A for hydroxyalkyl(meth)acrylate such that:(weight percent as cited below is based on the total weight of the finalphotopolymer):

(a) the total polyol content is preferably between 60 and 80 weightpercent in order for the final photopolymer to have good flexibility orelastomeric properties and

(b) the alkyldialkanolamine content is preferably 1-10 weight percent inorder to maintain good water developability and

(c) the hydroxyalkyl(meth)acrylate content is preferably 0.8-2 weightpercent so that good photocurability and hence good resistance to inkswell can be achieved.

1. Reaction of polyether or polyester diol (P) with the aforestatedstoichiometric excess of diisocyanate (Cy):

(i) In the case of polyether diol:

    HO-(-A--O--).sub.b H+ excess OCNR.sup.1 NCO→OCN-B-R.sup.1 -NCO(I-i)

where

A is --CH₂ CH₂ --, --CH₂ CH₂ CH₂ --, --CH₂ CH(CH₃)--, --CH₂ CH₂ CH₂ CH₂--, --CH₂ CH₂ CH(CH₃)--, or --CH₂ CH(CH₃)CH₂ -- or mixtures thereof;

B represents one or more segments of

    [-R.sup.1 -NH-C(:O)O(-A--O--).sub.b C(:O)NH-]

b is determined by the molecular weight of the polyether diol and isdiscussed in the description of polyether diol, below.

R¹ is a divalent aromatic, aliphatic, or cycloaliphatic group containing2-20 carbons, preferably 5-15.

(ii) In the case of polyester diol:

    HO-D-R.sup.2 OH+ excess OCNR.sup.1 NCO→OCN-R.sup.1 -E-NCO(I--ii)

where

D represents repeating segments of

    [-R.sup.2 --O--C(:O)-[(R.sup.3).sub.0 or 1 ]-C(:O)O-],

E represents one or more segments of

    [-NHC(:O)--O--D-R.sup.2 O-C(:O)-NH-R.sup.1 -]

R² is a divalent aliphatic, cycloaliphatic, or alpharyl group of 2-20carbons;

R³, when present (i.e., when R³ is 1), is a divalent aliphatic,cycloaliphatic, aryl or alpharyl group of 1-22 carbons.

When mixtures of polyether diols and polyester diols are used, the diolscan be used in any ratio.

These end-capping reactions are well known. As indicated, the terminalisocyanates on initially formed end-capped diols may react with otherhydroxyl groups on other polyether or polyester diols, therebyincreasing over-all molecular weight of the resulting polyurethane. Thisreaction is suitably carried out at conventional temperatures, e.g.,within the range of about 25°-80° C.

Chain extension of prepolymer product (I-i and/or I-ii) withalkyldialkanolamine (HO--R⁴ --R⁵ R⁶ --OH). In this operation, Reactions2 and 3 go forward together, the product II of Reaction 2 serving as anintermediate in Reaction 3:

2.

    OCN--R.sup.1 --OCN+HO--R.sup.4 --R.sup.5 --R.sup.6 --OH→ OCN--F--R.sup.1 --NCO                                     (II)

where

F represents one or more segments of

    [-R.sup.1 --NH--C(:O)--O--R.sup.4 -R.sup.5 -R.sup.6 --O--C(:O)NH--]

R⁴ and R⁶ are the same or different alkylene groups with 1-6 carbons; orR⁴ can be

--(CH₂ CH₂ O )_(d) CH₂ CH₂ -- provided R⁶ is --(CH₂ CH₂ O)_(e) CH₂ CH₂--, where d and e are each 0-9 and d+e=3-15;

R⁵ is -N(R⁷)-, -N N-, or -N(Ph)-; (Ph=phenyl)

R⁷ is an alkyl group with 1-6 carbons.

3.

I+HO-R⁴ -R⁵ -R⁶ -OH+II→OCN--R-R¹ --NCO

(Prepolymer III, or III),

where R comprises one or more segments of B and/or one or more segmentsof E; and one or more segments of F; which is to say, R comprises B, E,and F; or R consists essentially of B and F; or R consists essentiallyof B and E.

Reactions 2 and 3 are carried out in the same reaction mixturesubstantially simultaneously, at a temperature in the range of about25°-60° C., until all of the hydroxyl groups have reacted as determinedby titration of the remaining isocyanate. As indicated, individualpolymer chains in III may be expected to vary in the number of polyetherdiol, polyester diol, diisocyanate, and alkyldialkanolamine moieties.The reactant proportions are controlled within the ranges stated aboveso that all or substantially all polymer chains will terminate inisocyanate. This condition is essential for the fourth (and final) step.A small amount of residual free diisocyanate may be left after theformation of III.

In Reactions 2 and 3, note that the molar ratio, Cy/(P+N), is always>1.

Within III a preferred structure results when

R¹ is 4,4'-methylene diphenylene (MDI)

R⁴ and R⁶ are ethylene;

R⁵ is -N(R⁷)-;

R⁷ is methyl;

the diols include a mixture of an ethylene oxide end-cappedpolyoxypropylene diol and a polypropylene adipate diol where(-A--O--)_(b) has a molecular weight of about 1000-3500.

Prepolymer III and the herein described processes for synthesizing itare considered novel. Reaction 4. Reaction of chain-extended polymer(Prepolymer III) with hydroxyalkyl(meth)acrylate to give PhotopolymerIV:

III+HO-R⁸ --O--C(:O)--C(R⁹)=CH₂ →G-R-R¹ -G, (Photopolymer IV),

where

G is CH₂ =C(R⁹)--C(:O)--O--R⁸ --O--C (:O)--NH--,

R⁸ is 1-7 carbon alkylene, and

R⁹ is H or methyl.

Within IV a preferred structure results when R¹ is MDI;

R⁴, R⁶, and R⁸ are ethylene;

R⁷ and R⁹ are methyl;

R⁵ is --N(R⁷)-;

the diols include a mixture of an ethylene oxide end-cappedpolyoxypropylene diol and a polypropylene adipate diol where;

(A--O--)_(b) has a molecular weight of about 1000-3500.

The relationship of III and IV is readily evident in the structureJ-R-R¹ -J' where the J's are identical and are either -NCO (giving III),or G (giving IV).

This Reaction 4 is suitably carried out at a temperature in the range ofabout 60°-80° C., and is conveniently carried out following chainextension Reactions 2 and 3, in the same vessel. Consistent with III,Segments B and/or E, and F may be positioned at random in the polymerchains of IV. As indicated, most of the molecules comprise multiplemoieties of polyether (and/or polyester) diol, end-capping diisocyanate,and chain-extending dialkanolamine, with all or substantially allpolymer molecules of IV being terminated with alkylene(meth)acrylate.

The reactions described above can be carried out without a solvent, butpreferably are carried out in an anhydrous organic solvent. Suitablesolvents include methyl ethyl ketone, methyl isobutyl ketone, toluene,and mixtures thereof. The solvents should have a boiling point in therange of 80°-120° C. for easy casting of films and evaporation ofsolvent.

The following is a further description of the reactants.

The Diol (a) Polyether Diol

This product has the structure HO-(A-O)_(b) H where A is a divalentradical of ethylene, propylene, isopropylene, butylene, isobutylene; andb is such that the number average molecular weight of the group[A-O]_(b), or of the polymer diol (which is substantially the samething) is within the range of about 650-7,000, preferably about1,000-3,500. Polypropylene oxide glycol, MW about 1,000-3,500, orpolypropylene oxide end-capped with ethylene oxide, where the amount ofethylene oxide is 1-50 weight percent, preferably 10-30 weight percent,of the overall molecular weight, MW about 1,000 to 7,000, preferably1,000-4,000, are especially preferred. In the instance where copolymersare used, the idealized structure for A(O)_(b) would be --(CH₂ CH₂O)_(x) --(CH₂ CH(CH₃)-O)_(y) --(CH₂ CH₂ O)_(z) - where x+z and y aresuch that the ethylene oxide moiety represents about 1-50, preferably10-30, weight percent of the overall polyol molecular weight. Suchcopolymers include POLY G55- 37 (MW 2952, containing about 30 weightpercent of ethylene oxide), and POLY L 225-28 (MW 4000, containing about20 weight percent ethylene oxide); both available from Olin Corp. Thepolyether diol reactants may be made by processes well known in the artby reacting an alkylene oxide or mixtures of alkylene oxides with acompound having at least one active hydrogen atom, such as water;monohydroxylic alcohols such as ethanol and propanol; and dihydroxylicalcohols such as ethylene glycol and monoethyl ether of glycerine. Thepoly(oxyalkylene) products of such reactions will have linearoxyalkylene or oxyethylene-higher oxyalkylene chains, and such chainswill terminate with hydroxyl groups. Conventional potassium hydroxidecatalysts or double metal cyanide catalysts can be used.

(b) Polyester Diol

As noted, the polyester diol, HO-D-R² OH, where D and R² have the valuesabove given, may be used alone or in admixture with polyether diols.Suitable polyester diols include those made from dibasic acids orcaprolactones with an excess of glycol. The dibasic acids, which arepreferred, are those of the structure HO--C(:O)-[(R³)₀ or 1 ]--C(:O)OH,with an excess of glycol of the structure HO-R² -OH where R² and R³ areas above defined.

The molecular weight of D (or of the polyester diol, which issubstantially the same thing) should be about 600-6,000, preferablyabout 1,000-3,500.

Suitable dibasic acids include those of the saturated series, i.e.,oxalic, malonic, succinic, gluteric, adipic, pimelic, suberic, and thelike. In this group, adipic acid is preferred. Aromatic dibasic acidsinclude phthalic and terephthalic acids. In lieu of the acid itself, theanhydride may be used, e.g., phthalic anhydride, or its ester may beused, e.g., methyl terephthalate. Acid mixtures may be used. When R³ iszero the acid is of course oxalic. When R³ is "1," R³ contains 1-20carbons and the subsequent dibasic acid contains 3-22 carbons.

Suitable glycols for making the polyester diol include the alkyleneglycols, e.g., ethylene glycol, propylene glycol, trimethylene glycol,the three butane diols, tetramethylene glycol, isobutylene glycol,pinacol, and the like, including their mixtures. The diol may have acycloalkane structure or alkyl aromatic structure.

Useful polyester diols made from adipic acid include poly(diethyleneadipate) diol, poly(ethylene adipate) diol, poly(propylene adipate)diol, poly(propylene/ethylene) adipate diol, poly(butylene adipate)diol, poly(ethylene/butylene adipate) diol, poly(neopentyl adipate)diol, poly(hexane/neopentyl) adipate diol, poly(hexane adipate) diol,polycaprolactone diols and the like or mixtures thereof.

Processes for making polyester diols are well known. See, for example,Encyclopedia of Polymer Science and Engineering, John Wiley & Sons(1988), 2d Ed., Vol. 12, pp. 28-42, especially pp. 33-34; and Vol. 13,pp. 259-261.

The Diisocyanate

A wide variety of diisocyanates is available for end-capping thepolyether diol. These diisocyanates can be aliphatic, cycloaliphatic, oraromatic, with the structure OCN--R¹ NCO. The divalent radical R¹contains in general 2 to 100 carbon atoms and may optionally carrynon-interfering substituents such as ether groups, ester groups,urethane groups, amido groups, urea groups, aryl groups, aliphaticgroups, cycloaliphatic groups, or halogen atoms. Modified diisocyanatesare also usable. In one preferred embodiment, glycol modifieddiphenylmethane diisocyanate are particularly effective. Examples ofsuitable diisocyanates include 4,4'-methylene diphenyl diisocyanate(MDI), modified MDI, such as MDI reacted with a polyether polyol,available as Isonate 2181 from Dow Chemical Co., and MDI prepolymers,2,4-tolylene diisocyanate (toluene diisocyanate), 2,6-tolylenediisocyanate, mixtures of the two latter isomers, dimer of 2,4-tolylenediisocyanate, p-xylene diisocyanate, m-xylene diisocyanate,1,5-naphthalene diisocyanate, 3,3'-dimethylbiphenyl-,4,4'-diisocyanate,hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, lysinediisocyanate, isophorone diisocyanate,4,4'-methylenebis(cyclohexylisocyanate), methylcyclohexane-2,4 (or2,6)-diisocyanate, 1,3-(isocyanatomethyl)cyclohexane,m-tetramethylxylene diisocyanate, p-tetramethylxylene diisocyanate, andmixtures thereof.

Conventional urethane-forming catalysts may be used in the reactionswith diisocyanates. These catalysts include, e.g., organo-tin compoundssuch as dibutyl tin dilaurate and stannous octoate, organomercurycompounds, tertiary amines, and mixtures of these materials.

Alkyldialkanolamine

This material has the structure HOR⁴ R⁵ R⁶ OH, where the numbered R'sare as above defined. Within this group, methyldiethanolamine,bis(hydroxyethyl)piperazine, OHC₂ H₄ --N N--C₂ H₄ OH, andN,N'-Bis(2-hydroxypropyl)aniline, HO--CH(CH₃)CH₂ --N(Ph)--CH₂ CH(CH₃)OHare preferred. (Ph--phenyl.)

Hydroxyalkyl(meth)acrylate

This material has the structure HO-R⁸ OC(:O)--C(R⁹)=CH₂, where the R'sare as above defined. Within this structure hydroxyethylmethacrylate ispreferred.

Formulations with the Invention Photopolymer

The simplest formulation is the invention photopolymer plus an effectiveamount of photoinitiator. Such mixture can be solvent cast, as is, orthe solvent removed and the mixture extruded to create a solidphotopolymerizable layer on conventional backing materials. However, formany commercial uses it will be found preferable to formulate or extendthe photopolymerizable composition with about 1 to 30% by weight ofreactive (i.e., photoactive) monomer or oligomer, and most preferably inthe range of 5 to 15% by weight reactive monomer. Suitable reactivemonomers or oligomers are those of the formula:

    (CH.sub.2 =C(R.sup.9)--C(:O)--O--).sub.q -R.sup.10

where R⁹ is H or methyl, R¹⁰ is an organic moiety having a valence of q,and q is an integer.

Such reactive (meth)acrylate diluents include, but are not limited to,trimethylolpropane triacrylate, hexanediol diacrylate, 1,3-butyleneglycol diacrylate, diethylene glycol diacrylate, 1,6-hexanedioldiacrylate, neopentyl glycol diacrylate, polyethylene glycol 200diacrylate, tetraethylene glycol diacrylate triethylene glycoldiacrylate, pentaerythritol tetraacrylate, tripropylene glycoldiacrylate, ethoxylated bisphenol-A diacrylate, propylene glycolmono/dimethacrylate, trimethylolpropane diacrylate,di-trimethylolpropane tetraacrylate, triacrylate of tris(hydroxyethyl)isocyanurate, dipentaerythritol hydroxypentaacrylate, pentaerythritoltriacrylate, ethoxylated trimethylolpropane triacrylate, triethyleneglycol dimethacrylate, ethylene glycol dimethacrylate, tetraethyleneglycol dimethacrylate, polyethylene glycol-200 dimethacrylate,1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate,polyethylene glycol-600 dimethacrylate, 1,3-butylene glycoldimethacrylate, ethoxylated bisphenol-A dimethacrylate,trimethylolpropane trimethacrylate, diethylene glycol dimethacrylate,1,4-butanediol diacrylate, diethylene glycol dimethacrylate,pentaerythritol tetramethacrylate, glycerin dimethacrylate,trimethylolpropane dimethacrylate, pentaerythritol trimethacrylate,pentaerythritol dimethacrylate, pentaerythritol diacrylate,urethanemethacrylate or acrylate oligomers and the like which can beadded to the photopolymerizable composition to modify the cured product.Monoacrylates such as cyclohexyl acrylate, isobornyl acrylate, laurylacrylate and tetrahydrofurfuryl acrylate and the correspondingmethacrylates are also operable as reactive diluents, as well asmethacrylate oligomers such as epoxy acrylates, urethane acrylates, andpolyester or polyether acrylates.

Photoinitiators

The formulations comprising the novel materials of this inventionrequire a photoinitiator. A large number are available and useful.

Photoinitiators for the photopolymerizable composition and formulationscontaining the same include the benzoin alkyl ethers, such as benzoinmethyl ether, benzoin ethyl ether, benzoin isopropyl ether and benzoinisobutyl ether. Another class of photoinitiators are thedialkoxyacetophenones exemplified by 2,2-dimethoxy-2-phenylacetophenone,i.e., Irgacure®651 (Ciba-Geigy) and 2,2-diethoxy-2-phenylacetophenone.Still another class of photoinitiators are the aldehyde and ketonecarbonyl compounds having at least one aromatic nucleus attacheddirectly to the carboxyl group. These photoinitiators include, but arenot limited to benzophenone, acetophenone, o-methoxybenzophenone,acetonaphthalene-quinone, methyl ethyl ketone, valerophenone,hexanophenone, alpha-phenyl-butyrophenone, p-morpholinopropiophenone,dibenzosuberone, 4-morpholinobenzophenone, 4'-morpholinodeoxybenzoin,p-diacetylbenzene, 4-aminobenzophenone, 4'-methoxyacetophenone,benzaldehyde, alpha-tetralone, 9-acetylphenanthrene,2-acetylphenanthrene, 10-thioxanthenone, 3-acetylphenanthrene,3-acetylindone, 9-fluorenone, 1-indanone, 1,3,5-triacetylbenzene,thioxanthen-9-one, xanthene-9-one, 7-H-benz[de]-anthracen-7-one,1-naphthaldehyde, 4,4'-bis(dimethylamino)-benzophenone, fluorene-9-one,1'-acetonaphthone, 2'-acetonaphthone, 2,3-butedione, acetonaphthene,benz[a]anthracene 7.12 diene, etc. Phosphines such as triphenylphosphineand tri-o-tolylphosphine are also operable herein as photoinitiators.The photoinitiators or mixtures thereof are usually added in an amountranging from 0.01 to 5% by weight of the total composition.

Other Additives

The compositions may also contain other additives, which are known inthe art for use in photocurable compositions, e.g., antioxidants,antiozonants and UV absorbers. To inhibit premature crosslinking duringstorage of the prepolymer containing compositions of this invention,thermal polymerization inhibitors and stabilizers are added. Suchstabilizers are well known in the art, and include, but are not limitedto, hydroquinone monobenzyl ether, methyl hydroquinone, amyl quinone,amyloxyhydroquinone, n-butylphenol, phenol, hydroquinone monopropylether, phenothiazine, phosphites, nitrobenzene and phenolic-thiocompounds, and mixtures thereof. Such additives are used in an amountwithin the range of from about 0.01 to about 4% by weight of theprepolymer. These stabilizers are effective in preventing crosslinkingof the prepolymer composition during preparation, processing andstorage.

UV light absorbers, or UV light stabilizers, can be used to adjust thephotospeed and, therefore, exposure latitude of the polymer material.Numerous materials will be apparent to those skilled in the art.

The most important light stabilizer classes are:2-hydroxy-benzophenones, 2-hydroxyphenyl benzotriazoles, hindered aminesand organic nickel compounds. In addition, salicylates, cinnamatederivatives, resorcinol monobenzoates, oxanilides, and p-hydroxybenzoates are used as well. These additives are used in the range ofabout 0.09 to about 4% by weight of the prepolymer.

Tinuvin® 1130, a substituted hydroxyphenyl benzotriazole, available fromCiba-Geigy Corp., has been found to work exceptionally well.

The compositions also may contain up to about 50% by weight of an inertparticulate filler which is essentially transparent to actinic light.Such fillers include the organophilic silicas, bentonites, silica andpowdered glass. Such fillers can impart desirable properties to thephotocurable compositions and reliefs on printing plates containingthose compositions.

The compositions may also contain dye and/or pigment coloring agents.The colorants present in the photopolymer composition must not interferewith the imagewise exposure and should not absorb actinic radiation inthe region of the spectrum that the initiator, present in thecomposition is activatable.

The colorant may be chosen from among the numerous commerciallyavailable pigments and dyes. The coloring agent may be used in a solventsoluble form, or in the form of a dispersion. Where a particulatematerial is used, the particle size should be less than 5000 Angstroms.More preferably, the particles will be in the 200-3000 Angstrom range.

Although numerous pigments and dyes useful in the practice of thepresent invention will be apparent to those skilled in the art, a smallnumber of such materials are listed here.

Suitable pigments include the Microlith® series available fromCiba-Geigy. Especially preferred are the A3R-K and 4G-K materials.Suitable dyes include for example, Baso Blue 645 (C.I. Solvent Blue 4),Baso Blue 688 (C.I. Solvent Blue 81), Luxol Fast Blue MBSN (C.I. SolventBlue 38), Neopen Blue 808 (C.I. Solvent Blue 70), Orasol™ Blue 2GLN(C.I. Solvent Blue 48), Savinyl® Blue GLS (C.I. Solvent Blue 44),Savinyl Blue RLS (C.I. Solvent Blue 45), Thermoplast Blue 684 (C.I.Solvent Violet 13) and Victoria Blue BO (C.I. Solvent Blue 7). Blue andviolet are used in current applications but the color of the dye is notcritical. Other colors could offer advantages, including for example,resistance to fading.

Formulations using the photopolymers of this invention include thefollowing (in parts by weight):

(1) Photopolymer, about 50-100, preferably about 70-90;

(2) A mono-, di-, or multi-acrylate diluent, which can be a monomer oroligomer, about 0-25, preferably about 5-15;

(3) Photoinitiator, about 0.1-10, preferably about 0.5-2.0;

Organic solvent, 0 to about 200, preferably about 10-50.

(5) stabilizers, UV absorbers and colorants, 0.1 to 10, preferably about1-4, total.

Preparation of Plate

The photocurable composition can then be shaped and formed as a solidlayer of suitable thickness according to conventional solvent casting,i.e., dissolving the composition in a solvent, shaping the solution intoa film or plate and removing the solvent. Conventional extrusion,calendaring or hot press techniques can also be used. Solid layers ofthe photosensitive composition in the form of a film can be adhered tosupports such as those comprising polyester, nylon or polycarbonate.Other suitable supports include woven fabrics and mats., e.g., glassfiber fabrics or laminated materials made of, for example, glass fibersand plastics, and steel or aluminum coated plates. It is preferred thatthe supports are dimensionally stable and resistant to the washoutsolutions.

It is also usually necessary to protect photosensitive surfaces fromcontamination by dirt and dust during storage before being exposed andwashed. Such protection is accomplished by lamination or application ofa flexible protective cover sheet to the side of the photocurablecomposition opposite that of the support. In addition, the photocurablecompositions can sometimes be tacky and it is thus also desirable toapply a release film to the surface of the photosensitive layer beforeapplication of the coversheet. The release film consists of a thinflexible and water soluble polymeric film and allows for intimatecontact between the surface of the photocurable composition opposite tothe support and an image-bearing negative applied to the surface.

EXPOSURE AND DEVELOPMENT

Photosensitive articles comprising a support having a solid layer orsurface comprising the photocurable composition, e.g., solidflexographic printing plates, can then be processed by well-knowntechniques for imagewise exposure to actinic light. Preferably, thelight should have a wavelength of from about 230-450 microns. Exposureis through a negative placed between the light source and thephotosensitive surface. Suitable sources of light include Type RSsunlamps, carbon arc lamps, xenon arc lamps, mercury vapor lamps,tungsten halide lamps and the like.

Exposure periods depend upon the intensity of the actinic light,thickness of the plate and the depth of the relief desired on theprinting plate. Periods of from 1 to 20 minute exposures are preferred.

Development

After exposure and removal of the negative, the unexposed areas of thephotosensitive surface can be developed (removed) in aqueous washoutsolutions as herein described. This feature is particularly advantageousin that it avoids problems of disposing of washout solutions containingcommonly used organic solvents, such as chlorinated solvents, alcoholsor ketones. The washout solution should be slightly acidic and maycontain a surfactant. Dilute vinegar or citric acid solutions arepreferred. Useful acidic surfactants include sodiumalkynaphthalene-sulfonate, sodium alkylbenzene sulfonate, sodium alkylether sulfate, polyoxyalkylated alkylaryl phosphate ester sodium saltand the like. Overall additive concentrations are suitably 0.1-5%. Washtemperature can vary from 25-70° C. preferably at ambient temperature.Following washout, the plate may be postexposed for further hardening ofthe relief work.

EXAMPLES

The following examples illustrate without limiting the invention.

The raw materials used in the examples are described below:

    ______________________________________                                        Item      Description                                                         ______________________________________                                        TDI       Toluene (or tolylene) diisocyanate, 2,4                                       and 2,6-80/20 isomer mixture from                                             Aldrich Chemical Co., Inc.                                          Isonate 2181                                                                            Modified 4,4'-methylene diphenyl                                              diisocyanate from Dow Chemical Co.,                                           % NCO = 23.                                                         PPG 1025  Polypropylene oxide diol from Arco                                            Chemical Co.; MW = 1000.                                            Poly G 55-112                                                                           Polypropylene oxide/ethylene oxide diol                                       from Olin Corp., MW = 1000.                                         Poly G 55-37                                                                            ethylene oxide end-capped polyoxy-                                            propylene diol, hydroxyl number = 37,                                         MW = 3000 from Olin Chemical Co.                                    POLY L 225-28                                                                           ethylene oxide end-capped polyoxypropylene                                    diol, hydroxyl number = 28, MW = 4000,                                        from Olin Corp.                                                     S-108-46  Rucoflex S-108-46 is polypropylene                                            adipate diol from Ruco Polymer                                                Corporation, MW = 2400.                                             Irganox 1520                                                                            2,4-bis[(octylthio)methyl]-o-cresol used                                      as stabilizer, from Ciba-Geigy Corp.                                Irgacure 651                                                                            2,2-dimethoxy-2-phenylacetophenone, from                                      Ciba-Geigy Corp.                                                    ______________________________________                                    

EXAMPLE 1

166 g (0.95 moles) of TDI, 60 g of toluene, 160 g (0.16 moles) of a diolPPG 1025 and 53.2 g (0.05 moles) of a diol Poly G 55-112 were chargedinto a 2-liter resin kettle equipped with a nitrogen purge, air stirrerand thermocouple. The reaction mixture was kept at 35-40° C. for 19hours until an isocyanate content of 3.4 milliequivalents per gram ofsolution was reached. Then 19.2 g of Irganox 1520, 28 g of methyl ethylketone and 41 g of toluene were added. A solution containing 76 g (0.64moles) of methyldiethanolamine, 28 g of methyl ethyl ketone and 92 g oftoluene was then added to the reaction mixture in five portions over aperiod of 2.5-3 hours. At this point, an isocyanate content of 0.29milliequivalents per gram was obtained. 27.6 g (0.2 moles) ofhydroxyethylmethacrylate was then introduced into the reaction vesseland the temperature was raised to 60-70° C. The reaction was allowed toproceed for about 3-4 hours until the IR spectrum showed the absence ofan isocyanate peak at about 2260 cm⁻¹. 50 g of ethanol may also be addedto react with any trace amount of residual isocyanates left.

To 291 g of this polymer solution, 9.2 g of polypropylene glycolmonomethacrylate and 1.9 g of Irgacure 651 were added and mixed well.The solution was cast on a steel coated plate and dried, resulting in asolid, transparent polymer. A polyester coversheet coated with ahydroxyethylcellulose based release film was then laminated onto the topof the dry photopolymer. The photopolymer plate was then imaged for 5minutes and developed in a 0.25% acetic acid solution to yield aprinting plate with good reproduction of the negative film. A 20 milthick cured film of the above formulation exposed for 5 minutes has thefollowing properties: tensile strength of 1288 psi, modulus of 450 psi,elongation of 408%, Shore A of 72, resilience of 21 and 24-hour ambienttemperature swell in water, and aqueous based ink of 8.7% and 9.8%,respectively.

EXAMPLE 2

A two-liter resin kettle equipped with an air powered stirrer, anitrogen purge and a thermowatch was charged with 100 grams (0.266moles) of Isonate 2181, 196.3 grams (0.066 moles) of POLY G 55-37 and54.1 grams (0.022 moles) of Rucoflex S-108-46. The mixture was heated to60° C. for about 2 hours under vigorous stirring and then the reactionwas allowed to react for another 16 hours at 35° C. The reaction mixturewas then heated to 60° C. for another 4 hours until an isocyanate endpoint of about 1 milliequivalent per gram was reached (as determined bystandard titration with dibutylamine). Then 382 grams of toluene and 85grams of methyl ethyl ketone were added to the reaction vessel followedby the addition of 18.5 grams (0.155 moles) of methyldiethanolamine. Thetemperature of the reaction was then raised to 35° C. The reaction wasallowed to proceed for another 3-4 hours until the titration indicatedthat 0.05 milliequivalents of isocyanate groups per gram of solutionremained. 5.8 grams (0.044 moles) of hydroxyethylmethacrylate and 7.5grams of Irganox 1520 were then added. The reaction mixture was allowedto stir for another 16 hours after which there was no detectableisocyanate groups on the IR spectrum. The resulting polymer solution(designated as Polymer A) was a transparent, slightly yellow, viscousmixture.

Formulation A

A photosensitive composition was prepared by mixing 222 parts of PolymerA with 1 part (by weight) of Irgacure 651, 5 parts of diethyleneglycoldimethacrylate and 5 parts of an ethoxylated trimethylolpropanetrimethacrylate diluent (Sartomer 9035 from Sartomer Co.). Thecomposition was then solvent cast and dried to obtain a 67 mil solidphotosensitive plate. A water soluble release coating which waspreviously coated on a polyester film was then applied to the top of thephotopolymer layer. After removal of the polyester coversheet, the watersoluble release coating remained on the photopolymer plate. Aphotographic negative was then placed in contact with the plate and itwas imaged under vacuum by exposure under ultraviolet light. The platewas developed in an aqueous solution of 1 percent citric acid (or 2.5%acetic acid) to give a printing plate with a 30 mil relief having sharpimages and good reproduction of the negative.

A 20 mil cured film of this photosensitive composition has the followingphysical properties: tensile strength of 585 psi, modulus of 205 psi,elongation of 455%, shore A hardness of 39, resilience of 23. A 67 milplate of this formulation had good ink compatibility and swelled onlyabout 4 weight percent in aqueous based ink when soaked for 24 hours atambient temperature. The above plate composition showed excellent printdurability on press and good ink transfer with both aqueous and oilbased inks.

Formulation B

222 parts of the above Polymer A was also formulated with 1 part ofIrgacure 651, 2 parts of 1,6-hexanediol dimethacrylate, 2 parts oflauryl methacrylate, to give a photosensitive resin composition. Thesolution was then solvent cast into plates that were dried to form 67mil solid plates. The photopolymer plate was then processed as describedin Formulation example 1. It was developed in an aqueous solutioncontaining 1 part of vinegar and 1 part of water to give a 40 mil reliefprinting plate with sharp images and excellent reproduction of the artwork from the negative. The printing plate was used to print with bothwater and oil based inks with good ink transfer on different substrates.The plate's compatibility with aqueous and oil based inks was good as itswelled less than 5 weight percent when soaked in the inks for 24 hoursat ambient temperature. The toughness of the material resulted inexcellent print durability on press.

A 20-mil cured film of the above photopolymer composition has thefollowing physical properties: 392 psi for tensile strength, 189 psi formodulus, 568 for percent elongation, 44 for shore A hardness and 26 forresilience.

EXAMPLE 3

80 grams (0.213 moles) of Isonate 2181, 43.2 grams (0.0177 moles) ofRucoflex S-108-46, 165 grams (0.053 moles) of POLY G 55-37 and 0.023grams of dibutyltin dilaurate catalyst were reacted together in a1-liter resin kettle equipped with an air powered stirrer, a thermowatchand a nitrogen purge. The reaction mixture exothermed to about 40° C.and after about one hour, after which the exotherm has subsided, atitrated isocyanate content of 1 milliequivalent per gram of thereaction mixture was reached. 125 grams of toluene and 28 grams ofmethyl ethyl ketone were added. A solution containing 14.8 grams (0.124moles) of methyldiethanolamine dissolved in 125 grams of toluene and 28grams of methyl ethyl ketone was then added under vigorous mixing. Thetemperature was maintained at below 50° C. for about 3 hours or untilthe isocyanate content has reached 0.05 milliequivalents per gram ofsolution (as determined by titration). Subsequently, 6.2 grams ofIrganox 1520 dissolved in 63 grams of toluene and 14 grams of methylethyl ketone were added followed by the addition of 4.6 grams (0.035moles) of hydroxyethylmethacrylate. The temperature was raised to 70° C.for about 3-4 hours, until the infrared spectrum showed the completedisappearance of the isocyanate absorption at about 2260cm⁻¹. Theresulting product (designated as Polymer B) is a transparent, viscousliquid at 45 percent solids.

A photosensitive composition was prepared from Polymer B byhomogeneously mixing 444 parts of Polymer B with 4 parts of laurylmethacrylate, 4 parts of 1,6-hexanediol dimethacrylate and 2 parts ofIrgacure 651. The composition was solvent cast and dried to form 67 milsolid, clear and transparent plates. A water soluble release slip filmwas applied on the top of the photopolymer plate and the plate wasexposed under UV light through a negative, under vacuum. After exposure,the plate was developed in a dilute aqueous solution of vinegar(containing 1 part vinegar and 1 part water) at room temperature to givea good relief printing plate with excellent image quality andcompatibility with aqueous and oil based inks.

A 20 mil cured film of the above photosensitive polymer exhibitedtensile strength of 546 psi, modulus of 283 psi, elongation of 640percent, shore A hardness of 45, and resilience of 25.

EXAMPLE 4

A two-liter resin kettle was charged with : 80 grams (0.213 moles) ofIsonate 2181, 110 grams (0.0354) moles) of POLY G 55-37, and 145.2 grams(0.0354 moles) of Poly L 255-28 (from Olin Chemicals, prepared usingdouble metal cyanide catalysts to obtain low unsaturation and lowmonoalcohol content, as described in "Thermoplastic PolyurethaneElastomers Made From High Molecular Weight POLY-L Polyols" by C. P.Smith et al., J. Elastomers and Plastics,Vol. 24, p. 306, Oct. 1992).While purging with nitrogen, the mixture was heated to 70° C. for about6 hours under vigorous stirring. Heat was then turned off and thereaction was then allowed to proceed for another 16 hours at ambienttemperature. The reaction was titrated and an isocyanate end point of0.84 milliequivalents per gram was reached. 145 grams of toluene and 32grams of methyl ethyl ketone were added, while mixing. A solutioncontaining 14.8 grams (0.1241 moles) of methyldiethanolamine chainextender, 145 grams of toluene and 32 grams of methyl ethyl ketone wasadded. The reaction mixture was stirred vigorously while the temperaturewas maintained below 40° C. The reaction was allowed to proceed foranother 6 hours after which a significant increase in the viscosity canbe observed and an isocyanate content of 0.05 milliquivalents per gramof solution was left (as determined by titration). A solution containing72 grams of toluene, 16 grams of methyl ethyl ketone and 7.2 grams ofIrganox 1520 was added, while stirring, followed by 4.6 grams (0.035moles) of hydroxyethylmethacrylate. The reaction was allowed to proceeduntil the complete disappearance of the isocyanate peak at 2260 cm⁻¹ onthe IR spectrum. The resultant product was a transparent, viscous liquid(designated as Polymer C).

Formulation A

A photosensitive composition was prepared by mixing 200 parts of PolymerC with 0.84 parts of Irgacure 651, 1.7 parts hexanediol dimethacrylate,and 1.7 parts lauryl methacrylate. The solution was then solvent castand dried to form 67 mil solid and clear plates. A water soluble releaseslip film was applied onto the surface of the plates and then the plateswere exposed through a photographic negative under UV light and vacuum.After exposure, the plates can be developed in a 0.6% aqueous aceticacid solution to give a good relief printing plate with goodreproduction of the image. The composition also showed goodcompatibility with water and oil based inks. A 20-mil film of the abovecomposition has a tensile strength of 514 psi, modulus of 169 psi,elongation of 1208%, shore A hardness of 31, resilience of 38.

Formulation B

200 parts of Polymer C was mixed homogeneously with 4.2 parts of anaromatic acrylated urethane oligomer (Ebecryl 6700 from RadcureSpecialties Inc.), 1.7 parts of a C14-C15 methacrylate monomer (SR 2100from Sartomer Co.) and 0.84 parts of Irgacure 651 to form aphotosensitive composition. The solution was processed as describedabove and a printing plate with good relief image can be obtained whenwashed in an aqueous solution containing 0.6% acetic acid. The resultingprinting plate is a tough elastomeric material having tensile strengthof 493 psi, modulus of 181 psi, elongation of 695%, shore A of 36 andresilience of 36.

EXAMPLE 5

A one-liter resin kettle equipped with a thermowatch, a nitrogen purge,and an air-powered stirrer was charged with 80 grams (0.213 moles) ofIsonate 2181, 55 grams (0.018 moles) of POLY G 55-37, and 217.8 grams(0.053 moles) of POLY L 255-28. The mixture was heated to 70° C. andthen allowed to react until an isocyanate content of 0.8milliequivalents per gram was reached as determined by titration. 450grams of toluene was then added followed by 14.8 grams (0.124 moles) ofmethyldiethanolamine. The reaction was allowed to proceed for about 3hours while maintaining the temperature below 40° C. When an isocyanatecontent of about 0.04 milliequivalents per gram was reached, 100 gramsof methyl ethyl ketone and 7.4 grams of Irganox 1520 were added alongwith 4.6 grams (0.035 moles) of hydroxyethyl methacrylate. The reactionwas kept under vigorous stirring until the IR spectrum showed thecomplete disappearance of the isocyanate peak at about 2260 cm⁻¹. 50grams of methyl ethyl ketone was then added to reduce the viscosity andfacilitate mixing. A clear and transparent viscous solution was obtained(designated as Polymer D).

400 parts of Polymer D was formulated with 3.1 parts of hexanedioldimethacrylate, 3.1 parts lauryl methacrylate and 1.5 parts of aphotoinitiator, Irgacure 651. The solution was solvent cast and driedinto solid 60 mil plates. The resulting dry photosensitive plate wasthen protected with a release slip film and exposed under UV lightthrough a negative under vacuum. After exposure, the plate was developedin a 0.6 percent acetic acid aqueous solution using a brush type washoutunit to remove the unexposed area to give a plate with a 30 mil reliefwith excellent reproduction of the art work from the negative. Theresulting plate which is tough, resilient and elastomeric can be used asa printing plate and showed good compatibility with oil and water basedinks. A 20 mil cured film of the above photosensitive composition hasthe following properties: 440 psi for tensile strength, 196 psi formodulus, 963% for elongation, 40 for shore A hardness and 36 forresilience.

EXAMPLE 6

50 grams (0.133 moles) of Isonate 2181 and 181.5 grams (0.044 moles) ofPOLY L 255-28 were reacted at 70° C., under vigorous stirring in a1-liter resin kettle purged with nitrogen and equipped with athermowatch until an isocyanate content of 0.76 milliequivalents pergram was left. 248 grams of toluene was added along with 9.2 grams(0.077 moles) of methyldiethanolamine. The reaction temperature wasmaintained below 40° C. for about 3 hours until most of themethyldiethanolamine are chain extended and an isocyanate end point of0.04 milliequivalents per gram was obtained as determined by titration.55 grams of methyl ethyl ketone was added with 4.9 grams of Irganox 1520and 2.9 grams (0.022 moles) of hydroxyethylmethacrylate. The reactionwas allowed to proceed until no more isocyanate can be detected on theIR spectrum. 45 grams of toluene and 10 grams of methyl ethyl ketonewere also added to lower the viscosity for ease of handling. Theresulting product was a clear and transparent, viscous liquid,designated as Polymer E.

300 parts of Polymer E was mixed with 1.2 parts of Irgacure 651, 2.4parts of hexanediol dimethacrylate, and 2.4 parts of lauryl methacrylateto form a photosensitive composition. The solution was solvent cast anddried into 60 mil solid plates. A water soluble slip film was applied tothe top of the dry plate and then the plate was exposed under UV lightthrough a photographic negative. The plate was then washed in a 2.5%acetic acid aqueous solution to give a printing plate with sharp reliefimage. The tough and elastomeric plate can be used as a printing platefor aqueous and oil based inks printing. The properties of a 20 milcured plate are as follows: 367 psi for tensile strength, 219 psi formodulus, 803% for elongation, 42 for shore A hardness and 36 forresilience.

EXAMPLE 7

To 11,150g of Polymer A, prepared as in Example 2, was added 256gdiethylene glycol dimethacrylate, 256g Sartomer 9035, 51.2g Irgacure 651and 1.26g of Microlith® A3R-K pre-dispersed in MEK. This formulation wassolvent cast and dried to obtain a dry photopolymer layer. A watersoluble release coating was then applied to the top of the photopolymerplate. The plate was next imaged and developed in 2.5% acetic acidsolution at ambient temperature to give a printing plate with a reliefimage having good reproduction of the negative. A 20 mil thick dried andcured film of the formulated polymer gave identical physical propertiesto the un-colored material of Formulation A, Example 2.

EXAMPLE 8

To 11,150g of polymer solution, prepared as in Example 2, was added 256gdiethylene glycol dimethacrylate, 256g Sartomer 9035, 51.2g Irgacure 651and 1.14g of Microlith® 4G-K, pre-dispersed in MEK. Results areidentical to Example 7.

EXAMPLE 9

To 150 lbs of polymer solution (44.7% solids), prepared as in Example 2,was added 1.34 lbs hexanedioldimethacrylate, 1.34 lbs laurylmethacrylate, 0.67 lbs Irgacure 651 and 23g Tinuvin® 1130. (UVabsorber), and 6.46g Microlith® Blue 4G-K pre-dispersed in MEK. Thesolid photopolymer was prepared and tested as in Example 2, with goodresults.

What is claimed:
 1. A method of preparing a printing plate, the stepscomprisingblending about 50-100 parts by weight of a photocurablepolymer made by (I) reacting together in a solvent for the reactants, inthe mole ratios stated, modified MDI, 12 moles; ethylene oxide cappedpolypropylene oxide diol having a molecular weight of about 3,000, 3moles; polypropylene adipate diol having a molecular weight of about2400, 1 mole; thereby end-capping the diols with isocyanate; (II) thenadding to the reaction mixture of (I), methyl diethanolamine, 7 moles;continuing the reaction to chain extend the isocyanate-capped diols,thereby providing chain-extended isocyanate-capped diols terminatedinisocyanate groups; (III) adding to the reaction mixture of (II),hydroxyethylmethacrylate, 2 moles, and continuing the reaction to reactthe terminal isocyanate groups of (II) with the hydroxyl group of thehydroxyethylmethacrylate, thereby providing a photocurable polymer;with0 to about 25 parts by eight of a diluent selected from the groupconsisting of polypropylene glycol monomethacrylate, diethylene glycoldimethacrylate, hexanediol dimethacrylate, lauryl methacrylate,ethoxylated trimethylol propane trimethacrylate, aromatic acrylatedurethane oligomer, C₁₄ -C₁₅ methacrylate monomer mixture and mixturesthereof; about 0.1-10 parts by weight photoinitiator; about 0.002 to 8total parts by weight of stabilizers; a UV absorber which is asubstituted hydroxyphenyl benzotriazole, and a pigment having a particlesize less than 5000 angstroms, and 0 to about 200 parts by weight of ananhydrous organic solvent; casting the blend onto a plate substrate; anddrying the plate to remove the silver.
 2. A method of preparing aprinting plate, the steps comprisingblending about 50-100 parts byweight of a photocurable polymer made by (I) Reacting together in asolvent for the reactants, in the mole ratios stated, modified MDI, 12moles; ethylene oxide capped polypropylene oxide diol having a molecularweight of about 3000, 2 moles; ethylene oxide capped polypropylene oxidediol having a molecular weight of about 4000, 2 moles; therebyend-capping the diols with isocyanate; (II) then adding to the reactionmixture of (I), methyl diethanolamine, 7 moles; continuing the reactionto chain extend the isocyanate-capped diols, thereby providingchain-extended isocyanate-capped diols terminated in isocyanate groups;(III) adding to the reaction mixture of (II), hydroxyethylmethacrylate,2 moles, and continuing the reaction to react the terminal isocyanategroups of (II) with the hydroxyl group of the hydroxyethylmethacrylate,thereby providing a photocurable polymer; with 0 to about 25 parts byweight of a diluent selected from the group consisting of polypropyleneglycol monomethacrylate, diethylene glycol dimethacrylate, hexanedioldimethacrylate, lauryl methacrylate, ethoxylated trimethylol propanetrimethacrylate, aromatic acrylated urethane oligomer, C₁₄ -C₁₅methacrylate monomer mixture and mixtures thereof; about 0.1-10 parts byweight photoinitiator; about 0.002 to 8 total parts by weight ofstabilizers; a UV absorber which is a substituted hydroxyphenylbenzotriazole, and a pigment having a particle size less than 5000angstroms, and 0 to about 200 parts by weight of an anhydrous organicsolvent; casting the blend onto a plate substrate; and drying the plateto remove the solvent.
 3. A method of preparing a printing plate, thesteps comprising(I) Reacting together in a solvent for the reactants, inthe mole ratios stated,modified MDI, 12 moles; ethylene oxide cappedpolypropylene oxide diol having a molecular weight of about 3000, 1mole; ethylene oxide capped polypropylene oxide diol having a molecularweight of about 4000, 3 moles; thereby end-capping the diols withisocyanate; (II) then adding to the reaction mixture of (I), methyldiethanolamine, 7 moles; continuing the reaction to chain extend theisocyanate-capped diols, thereby providing chain-extendedisocyanate-capped diols terminated in isocyanate groups; (III) adding tothe reaction mixture of (II), hydroxyethylmethacrylate, 2 moles, andcontinuing the reaction to react the terminal isocyanate groups of (II)with the hydroxyl group of the hydroxyethylmeth-acrylate, therebyproviding a photocurable polymer;with 0 to about 25 parts by weight of adiluent selected from the group consisting of polypropylene glycolmonomethacrylate, diethylene glycol dimethacrylate, hexanedioldimethacrylate, lauryl methacrylate, ethoxylated trimethylol propanetrimethacrylate, aromatic acrylated urethane oligomer, C₁₄ -C₁₅methacrylate monomer mixture and mixtures thereof; about 0.1-10 parts byweight photoinitiator; about 0.002 to 8 total parts by weight ofstabilizers; a UV absorber which is a substituted hydroxyphenylbenzotriazole, and a pigment having a particle size less than 5000angstroms, and 0 to about 200 parts by weight of an anhydrous organicsolvent; casting the blend onto a plate substrate; and drying the plateto remove the solvent.
 4. A method of preparing a printing plate, thesteps comprising(I) Reacting together in a solvent for the reactants, inthe mole ratios stated, modified MDI, 12 moles; ethylene oxide cappedpolypropylene oxide diol having a molecular weight of about 4000, 4moles; thereby end-capping the diols with isocyanate; (II) then addingto the reaction mixture of (I), methyl diethanolamine, 7 moles;continuing the reaction to chain extend the isocyanate-capped diols,thereby providing chain-extended isocyanate-capped diols terminated inisocyanate groups; (III) adding to the reaction mixture of (II),hydroxyethylmethacrylate, 2 moles, and continuing the reaction to reactthe terminal isocyanate groups of (II) with the hydroxyl group of thehydroxyethylmeth-acrylate, thereby providing a photocurable polymer;with0 to about 25 parts by weight of a diluent selected from the groupconsisting of polypropylene glycol monomethacrylate, diethylene glycoldimethacrylate, hexanediol dimethacrylate, lauryl methacrylate,ethoxylated trimethylol propane trimethacrylate, aromatic acrylatedurethane oligomer, C₁₄ -C₁₅ methacrylate monomer mixture and mixturesthereof; about 0.1-10 parts by weight photoinitiator; about 0.002 to 8total parts by weight of stabilizers; a UV absorber which is asubstituted hydroxyphenyl benzotriazole, and a pigment having a particlesize less than 5000 angstroms, and 0 to about 200 parts by weight of ananhydrous organic solvent; casting the blend onto a plate substrate; anddrying the plate to remove the solvent.